Motor-control system



July 3, 1928.

T. P; KIRKPATRICK MOTOR CONTROL SYSTEM Filed Oct. 4, 1922 QLCQ Torque INVENTOR Thomas PKiPKPaTPiCK.

ATroRNEY Patented July 3, 1928.

[UNITED STATESIPATENT OFFICE.

THOMAS P. KIRKPATRICK, OF WILKINSBUHG, PENNSYLVANIA, ASSIGNOR TO WEST- i INGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENN- SYLVANIA.

MOTOR-CONTROL sYsrEiiL Application filed October 4, 1922. Serial No. 592,248.

My invention relates to motor-control systems, and it-has special relation to the control of motors for driving loads having unusually heavy fly-wheel effects, such as the spinning wheels of gyroscopes.

One object of my invention is to maintain substantially constant torque of the spinning motor durin the accelerating period.

Another 0 {ect of my invention is to prevent over-loat ing the motor during acceleration. I A further object of my invention is to accomplish the necessary control automatically and with increased efficiency relative to methods of the prior art. I

The ower system for operating the spinlieel of a gyroscope usually comprises a turbine-driven power generator for supplying I to an induction motor that is connected to the driving shaft of the spinning wheel. On account of thevery high inertia, it is necessary to accelerate the spinning motor very slowly. A scheme has been adopted in which the spinning motor is connected to the generator when at rest, and steam is gradually admitted The voltage and frequency of the. generator are gradually increased to normal as the turbine speedincreases. Manual control has been employed during. the entire accelerating period, which in some instances, consumed approximately two hours. During this period, it is desire able to maintain a substantially uniform power lII-Pllt into the motor with, however, a slight increase of power at low speeds.

The operator employs the ordinary instruments for measuring input and it will be recognized that, at low frequency, these instruments are unreliable.

I propose to employ a relay responsive to the motor current for automatically con to the turbine to start, the motor with a mimmum lmpressed voltage and frequency.

suitable condens'eror capacity device in series relation with the operating coil of the relay, and preferably connected to a shunt or resistor in series relation with the spinning-motor circuit, the relay coil and condenser being in shunt relation to the resistor. v

The relay is responsive to the current traversing the main circuit. At low frequency, the condenser has a higher impedance to the passage of alternating current than at normal frequency, and the relay coil therefor absorbs current in proportion to the frequency. The motor-operated throttlevalve is automatically controlled by the relay so as to permit a slight increase in the amount of steam admitted to the turbine during the early portion of the accelerating period.

My invention will be described in connection with the accompanying drawing, in which Fig. 1 is a diagrammatic representation of circuits and apparatus embodying my invention, and

Fig. 2 is a diagriunmatic representation of the relationsof current and torque in connection with the system of Fig. 1.

Referring particularly to Fig. 1, a spinning or a. fiy-wheel 1 of a gyroscope is directly connected to a spinning motor 2 of the induction type, which is supplied with current from a suitable generator'l; the

generator is driven by means of a turbine I or other suitable source of powerd.

-S'team or other fluid', under pressure, is admitted to the turbine 4 through'a throttle valve 5 which is actuated by a motor 6. A relay 7, having an operating coil 8, controls the direction of rotation of the motor 6. A condenser 9- is connected, in series relation with the coil 8, and both are disposed in shunt relation to a resistor 10 which is connected in circuit with the spinning motor 2. The motor 6 is supplied with power, from an auxiliary circuit comprising conductors 11 and 12, through a control switch 13.

Assuming the apparatus to be in the inactive or illustrated positions, in which the throttle valve 5 is presumed to be closed, the control switch 13 may be closed to admit current to the motor 6 through the relay 7 in its lower position. The motor 6 is so connected as to gradually open the valve 5 and admit fluid pressure to the turbine 4. The

- generator Bhegins to furnish power to the spinning motor 2 and, at a predetermined value of current traversing the operating coil8, the relay ,7. picks up, lnterrupting the circuit of the motor 6. If the accelerat ing current continues to rise, the relay 7 will be lifted to its upper position to reverse the direction of rotation of the motor 6 and partially close the valve 5. Nhen the value of the accelerating current is sufficiently decreased, the relay 7 again disconnects the motor 6 and, if insufficient power is then supplied to the motor 2,

the relay 7 is returned to its lower position to reconnect the motor 6 for a suflicient period of time to admit a greater supply of fluid-pressure to the turbine.

At low generating speed, and correspondingly low frequency, the condenser 9.p rovides a high impedance to current traversing the relay coil 8, whereas, at'higher frequencies, less impedance is offered to the passage of current. Therefore, as the spinning motor 2 approaches its normal speed, the relay 7 becomes more sensitiveand picks up at a lower value of current. Consequently, the

"motor 6 throttles the fluid-pressure to a current and torque at high frequency, for a given. capacity, of th Condenser It is apparent from the foregoing description that an automatic systemof the character described may be made much more efficient and effective than a system employing manual control. With my system of control the power apparatus may be of less capacity, with a corresp onding decrease in cost,'as compared to non-automatic systems in which the power input is of uncertain quantity. Other systems of power supply, such as motor-generator sets and rotary-converters, may be used instead ofa steam-driven unit. In such cases, a relay may be arranged to control the field strength of themotor or rotary converter ina manner corresponding to the control employed for the throttlevalve in the system that I have described.

I claim as my invention:

1. In a system of acceleration for flywheels, thecombination with a fly-wheeland a driving motor therefor, ofa variable speed alternating-current generator for supplying power to the motor, means for controlling the generator to supply a high accelerating current to said motor at low generator speed and automaticallyoperable means for controlling the generator to supply a lower cur rent to said motor at a higher speed.

2. In a system of acceleration for flywheels, the combination with .a fiy-wheel and a driving motor therefor, of a variable speed alternating-current generator for supplying power to the motor, means for controlling the generator to supply a high accelerating current to said motor at low generator speed'and means comprising a relay responsive to an increase in frequency of the generator for reducing the value of the current supplied to said motor.

3. In a system of acceleration for flywheels,the combination with a fiy-wheel and a driving motor therefor, of a variable speed alternating-current generator forsupplying the motor, means for controlling the generator'output and means responsive to a. change in the frequency of the generator for varying the setting of said control means 7 to further control thegenerator output.

4. In a system of acceleration for flywheels, the combination with a fly-wheel and a driving motor therefor, of a variable speed alternating-current generator for supplying power to the motor, current limiting means for controlling the generator output and a capacity device for automatically varying the setting of said current limiting means in'response to a change in the frequency of the generator current output.

5. In a system of acceleration for flywheels, the combination with a fly-wheel and a driving motor therefor, of a variable speed alternating-current generator for supplying power to themotor, current limiting means for controlling the generator output and means responsive to'a change in frequency of the generator for effecting a change in the operation of said current limiting means.

In testimony whereof, I have hereunto subscribed my name this second day of October,1922. r 1

' THOMAS P. KIRKPATRICK. 

